Topic 6: Plant structures and functions

Question 1

What happens during photosynthesis?

Answer 1

• Photosynthetic organisms use energy from the sun to make glucose.
• Some of this glucose is used to make larger, complex molecules that the plants need to grow.
• These make up the organism’s biomass - the mass of living materia
• Photosynthesis occurs in the Chloroplasts

Question 2

What’s the equation for photosynthesis?

Answer 2

Carbon dioxide + water —-> glucose + oxygen

(chlorophyll and light below and above the arrow)

Question 3

Explain the role of chloroplasts in photosynthesis?

Answer 3

• Contain chlorophyll which absorb light
• Energy is transferred to the chloroplasts by light

Question 4

What type of reaction is photosynthesis?

Answer 4

Endothermic - Energy is taken in during the reaction

Question 5

What are the limiting factors of photosynthesis?

Answer 5

• Light intensity
• CO2 concentration
• Temperature

Question 6

Light intensity’s affect on rate of photosynthesis core practical

Answer 6

1) Use a ruler to place a sealed conical flask with pondweed and water 15cm away from the lamp
2) Leave it for arounds 10 mins so the pondweed can adjust/photosynthesise
3) Connect the gas syringe to the conical flask and record the change in volume (oxygen)
4) Move lamp 10cm further away and repeat

Question 7

Explain the affect of light intensity on the rate of photosynthesis

Answer 7

• Light transfers the energy needed for photosynthesis
• At first, the rate of photosynthesis is directly proportional to light intensity, up to a certain point
• beyond this point, light intensity won’t make a difference and temperature or CO2 concentration will be the limiting factor

Question 8

Why wouldn’t you plot the photosynthesis against the ‘distance of lamp from plant’ when investigating light intensity on rate of photosynthesis? - what would you use instead?

Answer 8

• Use a light meter
• Distance from lamp and light intensity are inversely proportional

Question 9

What’s the inverse square law?

Answer 9

Light intensity is proportional to 1/distance squared

Question 10

Explain the affect of carbon dioxide concentration on the rate of photosynthesis

Answer 10

• As CO2 concentration increases, the rate of photosynthesis increases up to a certain point
• After this, the graph flattens out showing that CO2 concentration is no longer the limiting factor
• So, temp or light intensity must be the limiting factor

Question 11

Explain the affect of temperature on the rate of photosynthesis

Answer 11

• When temperature is the limiting factor, it’s usually because it’s too low, so the enzymes needed for photosynthesis work slower at lower temperatures
• But, if the plant gets too hot, the enzymes will denature (at 45’c)

Question 12

What are the two types of transport vessels found in plants?

Answer 12

Xylem and Phloem

Question 13

Explain the role of root hair cells in plants

Answer 13

• Cells on the surface of plant roots grow into ‘hairs’, which stick out into the soil
• Each branch of root is covered in millions of microscopic hairs
• This gives the plant a large surface area for absorbing water and mineral ions from the soil
• Mineral ions are absorbed by active transport against the conc gradient - the concentration of mineral ions is usually higher in the root hair cells than in the soil around them
• Water is absorbed by osmosis

Question 14

Explain the role of Xylem in plants

Answer 14

• Xylem tubes made of dead cells joined end to end with no end walls between them and a hole down the middle
• Strengthened with a material called lignin to prevent water pressure inside the vessels from bursting/collapsing them
• Carry water and mineral ions from the roots to the stem and leaves
• This movement of water from the roots, through the xylem and out of the leaves is called the TRANSPIRATION STREAM

Question 15

Explain the role of Phloem in plants

Answer 15

• Phloem tubes made of columns of elongated living cells with small pores in the end walls to allow stuff to flow through
• Transport food substances (mainly sucrose) made in the leaves to the rest of the plant for immediate use (e.g. in growing regions) or for storage
• This process is called TRANSLOCATION and it requires energy from respiration
• Transport goes in both directions

Question 16

Describe Transpiration in plants

Answer 16

• Caused by the evaporation and diffusion from a plant’s surface - most transpiration happens at the leaves
• Loss of water creates a slight shortage of water in the leaf, so more water is drawn up from the rest of the plant through the xylem vessels to replace it
• This means that more water is drawn up from the roots, so there’s a constant transpiration stream of water through the plant
• The transpiration stream carries mineral ions that are dissolved in the water along with it

Question 17

Explain the role of the stomata and guard cells in plants

Answer 17

• Stomata are tiny pores mostly found on the lower surface of leaves that allow CO2 and oxygen to diffuse directly in and out of a leaf
• In transpiration, water escapes through the stomata by diffusion
• Surrounded by guard cells that change shape to control the size of the pore
• Turgid guard cells = swollen with water so the stomata are open
• Flaccid guard cells = low on water and limp so the stomata are closed

Question 18

What are the environmental factors that affect transpiration rate?

Answer 18

Light intensity, Temperature, Air flow

Question 19

Explain the affect that Light intensity has on transpiration rate

Answer 19

Light intensity:
- The brighter the light, the greater the transpiration rate
- Stomata begin to close as it gets darker because photosynthesis can’t happen in the dark, so they don’t need to be open to let CO2 in
- When the stomata are closed, very little water can escape which reduces transpiration rate

Question 20

Explain the affect that Temperature has on transpiration rate

Answer 20

• As temperature increases, transpiration rate increases
• When it’s warm, the particles have more energy to evaporate and diffuse out of the stomata

Question 21

Explain the affect that Air Flow has on transpiration rate

Answer 21

• The better the air flow around a leaf (e.g. stronger winds), the greater the transpiration rate
• The water vapour is swept away from outside of the leaf, meaning that a low concentration of water is maintained, increasing rate of diffusion (high to low concentration) - this increases rate of transipration

Question 22

How can you estimate transpiration rate?

Answer 22

• Potometer measures the water uptake by a plant
  1) Set up apparatus with the tap shut off during the experiment
  2) Record the starting position of the air bubble
  3) Start a stop watch and record the distance moved by the bubble in a certain period of time e.g. ten minutes, to get the speed of the air bubble which is an estimation of transpiration rate

rate of transpiration = distance moved/time taken

Question 23

What’s the downside of using a potometer to estimate transpiration rate?

Answer 23

Only an estimate of transpiration rate as it assumes that water uptake of the plant is directly related to water loss from the leaves

Question 24

Name all parts of the leaf from top to bottom including how they are adapted

Answer 24

Waxy Cuticle - helps to reduce water loss by evaporation
Upper epidermis - Transparent so that light can pass through it to the palisade layer

Palisade layer - Chloroplasts near the top where they can get the most light for photosynthesis

Spongy mesophyll tissue - contains air spaces which increase rate of diffusion of gases

Xylem and Phloem - Provide leaf with water for photosynthesis and take away glucose produced. Also help support the structure.

Lower epidermis

Question 25

How are plants living in deserts adapted?

Answer 25

Small leaves/spines instead of leaves - Reduces surface area to reduce water loss by evaporation, spines prevent animals eating the plant to get water Curled leaves/hairs on surface of leaves - reduces air flow close to the leaf to trap water vapour near the surface, reducing diffusion of from the leaf to the air Thick waxy cuticles - Reduce water loss by evaporation Thick, fleshy stem - stores water Fewer stomata/stomata that can only open at night - reduce water loss by evaporation Stomata sunken in pits - stomata lower than leaf surface, reducing air flow, works in same way as curled leaves/hairs

Question 26

Describe auxins

Answer 26

- Plant hormones that control the growth at the tips and shoots aty the roots - Auxin is produced at the tips and diffuses backwards to stimulate cell elongation - Auxin promotes growth in the shoot but inhibits growth in the root - Involved in the growth responses of plants

Question 27

What happens when plant shoots are exposed to light?

Answer 27

POSITIVELY PHOTOTROPIC - Shoot accumulates more auxin on the shaded side - So, the cells grow faster on the shaded side which makes the shoot bend towards the light - The shoot bends towards the light to absorb more light for photosynthesis, enabling the plant to grow

Question 28

How are shoots affected by gravity?

Answer 28

NEGATIVELY GRAVITROPIC (grow away from gravity) - When a shoot grows sideways, gravity produces an uneven distribution of auxin at the tip so there's more auxin on the lower side - This causes the lower side to grow faster, bending the shoot upwards

Question 29

What happens when roots are exposed to light?

Answer 29

NEGATIVELY PHOTOTROPIC - More auxin accumulates on shaded side - The auxin in roots inhibits cell elongation, so the root bends downwards back into the ground

Question 30

How are roots affected by gravity?

Answer 30

POSITIVELY GRAVITROPIC (grow towards gravity) - More auxin on its lower side - Extra auxin in the roots inhibits growth, so the cells on top elongate faster, causing the root to bend downwards

Question 31

What are the commercial uses of auxins?

Answer 31

Selective weedkillers developed from auxins affects broad leaved plants only which disrupts their growth patterns, killing them whilst the grass and crops are untouched Rooting powder contains auxins so when added to cuttings, they produce roots and start growing as new plants. This enables growers to produce clones of good plants quickly

Question 32

What are the commercial uses of Gibberellins?

Answer 32

Gibberellins stimulate seed germination, stem growth and flowering. So, plants can flower out of season. It can reduce flower formation to improve fruit quality When applied to unpollinated flowers, fruit will grow but the seeds won't (producing seedless fruit) Seeds can be treated with gibberellins so they can germinate when they wouldn't normally and all the seeds can germinate at the same time

Question 33

What's the commercial use of ethene?

Answer 33

Increases ripening so that they are perfect by the time they reach supermarket shelves

Question 34

Where are stomata found?

Answer 34

- lower surface of leaves